Aqueous ink compositions

Abstract

The invention provides an aqueous printing ink composition comprising a polyurethane dispersion, wherein the polyurethane of the polyurethane dispersion comprises the properties of (a) ketone or aldehyde groups present at one or more polymer chain ends; (b) a number average molecular weight ≤50,000, more preferably ≤25,000 and; (c) the content of ketone and/or aldehyde groups is in the range 0.02 to 4.0 mmol g−1, based on the dry polymer weight.

The invention claimed is: 
     
       1. An aqueous printing ink composition comprising a polyurethane dispersion, wherein the polyurethane of the polyurethane dispersion comprises the properties of (a) ketone or aldehyde groups present at one or more polymer chain ends; (b) a number average molecular weight ≤50,000, more preferably ≤25,000 and; (c) the content of ketone and aldehyde groups is in the range 0.02 to 4.0 mmol g −1 , based on the dry polymer weight. 
     
     
       2. The composition of  claim 1 , wherein the groups present at one or more polymer chain ends are ketone groups. 
     
     
       3. The composition of  claim 1 , wherein the polyurethane is predominantly linear in structure and the average number of ketone and aldehyde groups on the polymer is two or less. 
     
     
       4. The composition of  claim 1 , wherein the polyurethane dispersion has an acid value of ≥10 mgKOH g −1  based on the dry polymer weight. 
     
     
       5. The composition of  claim 1 , wherein the polyurethane dispersion further comprises a reagent that may react with the ketone or aldehyde groups at the one or more polymer chain ends to cure the composition. 
     
     
       6. The composition according to  claim 5  wherein curing occurs via linear chain extension. 
     
     
       7. The composition of  claim 5  in which the reagent is a difunctional, trifunctional or higher functional primary diamine, or dihydrazide, and where such reagent is preferably a difunctional reagent. 
     
     
       8. The composition of  claim 7  in which the difunctional reagent is adipic dihydrazide. 
     
     
       9. The composition of  claim 1 , wherein the polyurethane of the polyurethane dispersion further comprises hydroxyl groups and where the hydroxy value of the polyurethane is preferably ≤100, and more preferably ≤50 mgKOH g −1 . 
     
     
       10. The composition of  claim 9 , where the hydroxyl groups are present at one or more polymer chain ends. 
     
     
       11. The composition of  claim 1 , comprising ≤25% (w/w) of any blend of solvent with boiling points ≥150° C. and heats of vaporization ≥500 J g −1 . 
     
     
       12. The composition of  claim 1 , further comprising an additional styrene-acrylic dispersion. 
     
     
       13. The composition of  claim 1 , wherein the polyurethane is anionically stabilized by including a carboxylic acid into the polyurethane chain. 
     
     
       14. The composition of  claim 13 , wherein the anionically stabilized polyurethane is neutralized with a tertiary amine, potassium hydroxide or sodium hydroxide. 
     
     
       15. The composition of  claim 14  wherein the anionically stabilized polyurethane is neutralized with a tertiary amine having a boiling point of greater than 125° C. 
     
     
       16. The composition of  claim 14 , wherein the anionically stabilized polyurethane is neutralized with triethylamine or N,N-dimethylethanolamine, preferably N,N-dimethylethanolamine. 
     
     
       17. A method for printing an article, comprising printing the composition of  claim 1  onto a substrate and curing. 
     
     
       18. The method of  claim 17 , wherein the substrate is suitable for the printing of packaging, food packaging, metal substrates, textiles, decor laminates and graphics. 
     
     
       19. A printed article comprising the composition of  claim 1 .